Nowadays natural rubber (one example of polyisoprenoids) for use in industrial rubber products can be harvested from Hevea brasiliensis (Para rubber tree) belonging to the family Euphorbiaceae.
Natural rubber is found mainly in the latex produced in specific cells called latex vessels of rubber trees, and the latex is processed to produce natural rubber. The latex is generally harvested from rubber trees by making groove-like incisions in the trunk of the trees (tapping) and collecting the latex as it oozes from the cut latex vessels.
Natural rubber exists in the form of particles in the latex. It has a particle size distribution with plural peaks, which indicates that rubber particles of different sizes are present in natural rubber latex (Non-Patent Literature 1). Further, it has been reported that the rubber synthesis activity of rubber particles differs depending on particle size; rubber particles having a smaller particle size have higher rubber biosynthesis activity than rubber particles having a larger particle size.
Since the characteristics of rubber particles in the latex differ depending on particle size as described above, in order to prepare rubber particles having preferable properties from the latex it is ideal to fractionate rubber particles from the latex by particle size to prepare a natural rubber latex having a high content of rubber particles of a desired size.
However, it has been difficult to fractionate a large amount of rubber particles in the latex by particle size with high accuracy. For example, since rubber particles aggregate very easily, when gel permeation chromatography or other techniques usually used for fractionating proteins or the like by size are used, the throughput is low and it is thus very difficult to fractionate a large amount of rubber particles by particle size with high accuracy.
Rubber particles may be fractionated by particle size using antibodies (Patent Literature 1). This method, however, involves preparing different antibodies that bind to each of the proteins on different sized rubber particles.
As for natural rubber, there are many studies focused on the rubber synthesis activity of rubber particles, and it is important to maintain the rubber synthesis activity of rubber particles. However, when the latex is stored as it is, problems such as aggregation of rubber particles or brown discoloration occur, resulting in impairment of the rubber synthesis activity of the rubber particles. Therefore, there is also a need for a method which can acquire rubber particles without impairing their rubber synthesis activity.